1. Field of the Invention
The present invention relates to a procedure for the processing of an unexpected disconnect re quest, as defined in the preamble of claim 1.
2. Description of Related Art
For the connection of subscribers to a local exchange in a data communication network, a generally known method is one whereby subscribers are connected to a local network whose access node is connected to the local exchange.
Open interfaces (V5.1 and V5.2) between an access node and a local exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards of the ETS 300 324 and ETS 300 347 series. V5 interfaces enable subscribers belonging to a physically separate local network, either wired or wireless, to be connected using the standard interface of the telephone exchange. A dynamic concentrator interface V5.2 consistent with the ETS 300 347-1 and 347-2 standards, consists of one or more (1-16) PCM (Pulse Code Modulation) lines. One PCM line contains 32 channels, each with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s in all. The V5.2 interface supports analogue telephones as used in the public telephone network, digital subscriptions, such as ISDN (Integrated Services Digital Network) basic and system subscriptions as well as other analogue or digital terminal equipment based on semi-fixed connections.
In a wireless local loop (WLL), a terminal device is connected via a wireless link to an access node (AN) or a WLL controller. The access node may consist of multiplexers, crossbar switches and various transmitting systems. The WLL system may be based e.g. on technology used in mobile telephone systems, such as the GSM/DCS1800 technology (GSM, Global System for Mobile Communications; DCS, Digital Cellular System). GSM is a European digital mobile communication system standardised by ETSI. DCS-1800 is a mobile communication system standardised by ETSI, which is based on the GSM specification and aims at a more effective use of microcells and which works in the frequency range of 1800 MHz. Between the terminal device and the access node there is a base station, through which call signals sent by the terminal device over a radio channel are transmitted via the access node to a public telephone network and vice versa. The access node or WLL controller can be connected to the telephone exchange using e.g. a V5.1 or V5.2 interface.
PSTN signalling (PSTN, Public Switch Telecommunication Network), analogue subscribers, over a V5 interface is nationally defined in each country. For this reason, the signalling at the time of call setdown may vary somewhat, depending on the country where the communication system is being operated.
According to the V5 specification, a local exchange may send a disconnect message to the access node to initiate call setdown. According to the specification, the disconnect message causes disconnection of the call and release of the resources reserved for the call both in the access node and in the local exchange.
Call setdown is normally initiated only after the subscriber has hung up. If the subscriber does not hang up after the call has been finished, then the local exchange may send the access node a signal message indicating that it is expecting the subscriber to hang up and that the voltage supply to the subscriber can be interrupted. After this, if the subscriber continues to keep the receiver lifted, then, upon the lapse of a standard time-out period, the local exchange will send the access node a disconnect message, whereupon the access node acknowledges the disconnect message.
This results in a serious conflict. In the local exchange, all resources have been released, but the subscriber is keeping the receiver lifted. This is an undefined condition. In this situation, a new setup request for a call to the subscriber may be received although the subscriber has not hung up to close the previous call.